Super Jet 701 SuperJet, Cant start, Explodes in exhaust, Wet sparks

[nicolajjetrider]

Hi all.

My friend has a SuperJet 701 98' .

It is all stock. When he bought it it startet fine, but you needed to pump the throttle to get som rpm's in it. After first run we triend to injust the lowspeed a littel, with that resault that it would start at all, then we triend to injust it back ( 1/4 ) but still not start.

But as more that we turned the engine, the more gas of course, then it suddenly exploded in the exhaust ( every time we tried pushing the start buttom ).

--- We agreed that the carbs maybe needed a rebuild kit, so that he bourght, and rebuilded the carbs.

Now: HUGE explosion in the exhaust. And the engine will not even give a littel fart for life. It turnes FINE and have 10.5 Bar compression on both cylinders.
When I look at the gas filter i cant see the engine suges gas in it.
When we try with ( start Gas ) it whont start, but after som tries, explosion in the exhaust will happen.

Very Good Spark on the new plugs!

It looks like every time we take the sparks out, they are very WET! ( gas )

The carbs are injustet:
1 Turn out and 1/4 on the high speed
1 Turn Out and 1/2 on the low speed.

What do you think there is wrong?

Nicolaj

 

[jetpilot08]

Is there a primer on the ski? I had a primer a while back that leaked gas into the rear cylinder. If it sat for a few days It would blow a chit ton of fuel out of the exhaust. Luckily no explosions. Maybe the needle and seats in the carbs are leaking by. Were those replaced when he rebuilt the carbs?

 

[sjetrider]

almost sounds like a serious compression issue. If not the check consistancy of the spark while utrning it over. Mane sure it does not spark only when you let off or initially hit the start button and not while turning it over. This could be in ss switch.

 

[swapmeet]

This is a long shot, but make sure the feed line and return line arn't swapped.

My buddy had this happen and filled the cylinders with gas.

After that would be needle and seat, remove flame arrestor and look down carb while cranking. See if you have a dribbler, replace needle and seat on that carb (if twin carb).

 

[Polish jet pilot]

you are running RICH - decrease LOW speed

 

[Matt_E]

I'd pull the flywheel off and see if the key is sheared. Sounds to me like the timing is off for some reason.

 

[tor*p*do]

verify it has spark when cranking
also unplug and test the start stop switch
I have seen these where there is no spark while cranking and then spark as you let off the start switch and that can result in boom

 

[rickytx1981]

I agree with Matt. I had the same issues last season tuned out to be a sheared key. My engine ran rough at first and slowly got worst till all it would do was backfire, sounded like a shotgun and scared the crap out of my neighbors.

 

[rickytx1981]

opps sorry old thread

 

[701SJFMT]

your wood drift key is shered off. matt e is right